For manufacturing semiconductor circuits, various transporting and processing steps are consecutively applied to semiconductor wafers (diameter e.g., 300 mm). While the wafer is usually transported in a clean room at room temperature (e.g., 20 . . . 30.degree. C.), the wafer is often processed at a substantially higher process temperature (e.g., 300 . . . 500.degree. C., depending on the process), for example, to deposit a film by well-known techniques (e.g., chemical vapor deposition CVD). For processing, the wafer is placed on a chuck that is usually at process temperature.
However, changing the environment temperature of the wafer rapidly from room temperature to process temperature causes immediate wafer expansion, widely referred to as thermal shock. Due to intrinsic impurities and contamination in the silicon, the heat propagates in the wafer unequally causing further unwanted effects like wafer bowing, misplacement on the chuck, or breakage. In other words, placing the cold wafer on the hot chuck surface should be avoided.
Load-lock systems that couple the clean room and the processing chamber can stepwise increase the environment temperature of the wafer. However, using the load-lock system for preheating is sometimes not desired so that the following scheme is used instead:
In a first step, the wafer is transported into the processing chamber and placed near the chuck; in a second step (heating up, soaking up), the environment temperature near the wafer is increased by a heater block so that the wafer is preheated to the process temperature (e.g., during 90 seconds); and in a third step, the wafer is placed on the chuck and processed.
This scheme reduces mechanical stress and thermal shock of the wafer; however, the chamber is evacuated so that in the heating up step, the heater block can transfer heat substantially only by radiation. Also, the chamber is temporarily prevented from processing, thus reducing the throughput. In other words, the expensive chamber is booked for the low value adding heating up step for an undesired long time.
The present invention seeks to provide apparatus and method which mitigate or avoid these and other disadvantages and limitations of the prior art.